5.3.1 Transition Elements & 5.3.2 Qualitative Analysis: Module 5: Physical Chemistry & Transition Elements: Chemistry OCR A A Level

Define a transition element

A d block element that forms at least one stable ion with partially filled d subshel.

Where are the transition metals located in the periodic table?

In the middle block from Ti to Cu.

What are the 2 elements in d block that are not considered as transition metals?

Scandium and zinc.

Why is scandium and zinc not considered as transition metals?

Scandium only forms Sc ^3+ , where the d orbitals are empty.

Zinc only forms Zn^2+ where the d orbitals are full.

Which electrons do transition metals lose first when forming ions?

4s

What are some characteristic physical properties of transition metals?

● Metallic

● High density

● High melting and boiling point

● Shiny

● Good conductors of heat and electricity

What are the characteristic chemical properties of transition metals (4)?

● Variable oxidation states → take part in many redox reactions

● Coloured compounds/ions in solution

● Good catalysts

● Form complex ions

In potassium manganate (VII), what is the oxidation number of Mn?

Mn = +7

What are the 2 main ways in which transition metals act as an effective catalyst?

● They provide a surface on which reaction can take place.

● They change oxidation states to form intermediates required for pathways with lower activation energy.

Give some examples of transition metal catalysts and the processes/reactions they catalyse (4)?

● Iron - Haber process

● Vanadium (V) oxide - contact process

● Nickel - hydrogenation of alkenes

● Manganese (IV) oxide - decomposition of hydrogen peroxide

● Copper sulfate - hydrogen production

What is a complex ion?

Transition metal ion bonded to one or more ligands by coordinate bonds.

Define a ligand.

Molecule or an ion that can donate a pair of electrons to the metal to form a coordinate bond.

What is a coordinate bond?

A bond in which one of the atom provides both the electrons required for bonding, also known as dative bonding.

What does the coordination number indicate?

The number of coordinate bonds formed between the metal ion and its ligands.

What is a mono/unidentate ligand?

A ligand that forms one co-ordinate bond to the central metal ion (one lone pair to donate).

What is a bidentate ligand?

A ligand that forms two coordinate bonds to the central metal ion (2 lone pairs to donate).

What is a multidentate ligand?

A ligand that forms three or more coordinate bonds to the central metal ion.

Name the most common bidentate ligand.

Ethane-1,2-Diamine

How many coordinate bonds does EDTA^4- form?

Six (6)

EDTA is a chelating agent, what does that mean?

EDTA decreases the concentration of metal ions in the solution by binding to them and forming complex ions.

If a transition metal ion has 2 ligands, what shape is it usually?

Linear

If a transition metal ion has 4 ligands, what shape is it usually?

Tetrahedral

Name an exception to the general rule that ions with 4 ligands is generally tetrahedral. What shape is it?

Platin is square planar → Forms cisplatin

What shape is a complex ion if it has 6 ligands?

Octahedral

How can complex ions display E-Z or cis-trans isomerism? What shapes of ions does this apply to?

Ligands differ in the way in which they are arranged in space 2 ligands of the same type can be on the same side of the metal ion (next to each other), which forms the E or cis isomer 2 ligands of the same type can be on opposite sides of the metal ion (not next to each other), which forms the Z or trans isomer Applies to square planar and octahedral complex ions.

What conditions are needed for a complex ion to display optical isomerism?

Usually applies to octahedral molecules with 2 or more bidentate ligands, so that the mirror images are non superimposable.

What is cis-platin used for? Describe its mechanism of action.

It is used as an anti-cancer drug. It binds to DNA of fast-growing cancer cells and prevents cell division, hence reducing the growth of cancer.

Which metal ion is present in a haem group?

Fe^2+

What is the coordination number of a haem group?

6

What are the ligands in haem group?

4 nitrogen forming the porphyrin ring

1 oxygen

1 globin

What is a precipitation reaction?

A reaction where soluble ions in separate solutions are mixed to form an insoluble compound.

Why are redox titrations with transition metal compounds said to be self-indicating?

They usually involve a colour change as the metal is changing oxidation state; sometimes an indicator is still needed/useful.

Describe how to test for metal ions.

● Fill half of the test tube with the sample.

● Add aqueous ammonia or sodium hydroxide drop by drop.

● Colour of precipitate indicates the ion present.

Write the method used to test for ammonium ions.

● Fill half the test tube with sample.

● Add sodium hydroxide and warm gently.

● Smelly gas is produced; damp red litmus paper turns blue.

Why does lime water turn milky in the presence of carbon dioxide?

When carbon dioxide is bubbled in calcium hydroxide (lime water), calcium carbonate precipitate is formed.